1. Field of Invention
The present invention relates to a method of manufacturing an active matrix organic light emitting diode (OLED). More particularly, the present invention relates to a method of preventing the cathode of an active matrix organic light emitting diode from breaking.
2. Description of Related Art
Organic light emitting diode (OLED) is a semiconductor device capable of converting electrical energy into light energy with a high conversion efficiency. The most common applications include indicator lights, display panels and optical pick up heads. Because OLED has some special properties such as wide viewing angle, ease of manufacture, low production cost, high response speed, wide range of operating temperature and full coloration, OLED is a suitable candidate for forming multimedia display devices.
At present, the active matrix type of OLED is being rapidly developed. In the following, a method of manufacturing a conventional active matrix OLED is described. FIG. 1 is a schematic cross sectional view showing the structure of a conventional active matrix OLED.
A conventional active matrix OLED as shown in FIG. 1 is formed in several steps. First, a gate electrode 102 is formed over a substrate 100 and then a gate insulation layer 104 is formed over the substrate 100 and the gate electrode 102. A channel layer 106 is formed on the gate insulation layer 104 above the gate electrode 102. Thereafter, a drain terminal 108a and a source terminal 108b are formed over the channel layer 106 to form a thin film transistor.
A passivation layer 110 is formed over the substrate 100 covering the thin film transistor. An opening 112 that exposes the source terminal 108b is formed in the passivation layer 110. Thereafter, an anode layer 114 is formed over the passivation layer 110 and the interior of a portion of the opening 112 so that the anode layer 114 and the source terminal 108b are electrically connected. A light-emitting layer 116 and a cathode 118 are sequentially formed over the substrate 100. Ultimately, an active matrix organic light emitting diode is formed over the substrate 100.
In a conventional method of forming an active matrix OLED, both the organic layer 116 and the cathode layer 118 are formed over the thin film transistor structure and the anode layer 114 through an evaporation-deposition process. However, step coverage capacity of the organic layer 116 and the cathode layer 118 is poor. Hence, sharp corners 120 within the thin film transistor structure such as the ones at each end of the source/drain 108a/108b may break or form a discontinuity after forming the organic layer 116 and the cathode layer 118. When the anode layer 118 is discontinuous or has a break, current conduction within the device as well as emissive power of the device is severely affected.